1. Field of the Invention
The present invention relates to a fundus camera used for photographing a fundus of a subject's eye in an ophthalmologist's office or the like.
2. Description of the Related Art
Hitherto, techniques for facilitating focusing a fundus camera on a subject's eye have been known. For example, first, a focus split target is projected onto the pupil of a subject's eye, on which split images of the focus split target are formed. Then, the split target images are observed via a focusing lens of an observing/photographing system. Thus, focusing is performed by observing a positional relationship of the focus split target images.
Japanese Patent Application Laid-Open No. 5-95907 discusses a known fundus camera that captures projected focus split images and that performs autofocusing based on the positional relationship of the focus split images. More particularly, the fundus camera captures two split images of a focus split target projected onto a fundus and detects a focus state based on positions of the two focus split target images. At that time, brightness of the target is attenuated.
Further, Japanese Patent Application Laid-Open No. 8-275921 discusses an ophthalmologic apparatus that projects a focus target onto a fundus of a subject's eye and captures a target image using a photographic optical system to detect a focus state.
Hitherto, a fundus camera has been known, which has a unit for projecting a light flux of a focus split target onto a fundus of a subject's eye, on which split images of the focus split target are formed, and a unit having a focusing lens for observing/photographing the fundus. Both of the units can be moved in the direction of an optical axis interlockingly with each other. Then, focus split target images formed on the fundus of the subject's eye are observed and brought into a predetermined positional relationship, for example, aligned with each other. Thus, the fundus camera can easily be focused on the fundus of the subject's eye. In addition, an apparatus has been known, which captures focus split images and performs autofocusing by detecting the position of each focus split image.
However, to eliminate reflection light from the cornea of a subject's eye, conventional fundus cameras are constructed such that a fundus illumination light flux or a focus slit target light flux and an observing/photographing light flux are respectively incident upon different areas in the vicinity of the pupil of a subject's eye. Accordingly, in a case where an aberration of an optical system of a subject's eye varies among individuals, when the fundus of a subject's eye is photographed only with the positions of the focus split target images set in a predetermined positional relationship, a focusing error may be caused depending on subject's eyes. Consequently, a fundus image may be out of focus.